In the arts of preparing cushion structures, foamed polyurethane material is well used to form automobile or airplane seats and the like.
However, foamed polyurethane seats have problems that the chemicals used in the process of its production are difficult to handle and that freon is discharged. Furthermore, because the compression characteristics of foamed polyurethane seats show a unique feature that it is hard at the initial stage of compression and then abruptly sink down, it not only is scanty in the cushioning property but also gives a strong "bottom-hit feel". Still more, the seats have little air-permeability and consequently is apt to become stuffy, which renders the seats objectionable as cushion structures in many cases. On top of it, foamed polyurethane seats are soft and have little resilient power against compression because it is foamed. The resilient power can be improved by increasing ensity of foamed seats, but such also increases the weight and invites a fatal defect that its air-permeability is still aggravated.
Further, foamed urethane seats generate poisonous gases when it is burned out in the furnace and it is difficult to use for recyclable material, then it is longed new material made of the fibers aggregate for the cushion structure instead of foamed polyurethane seats.
For producing said cushion structures in order to replace said foamed polyurethane seats, it has been widely practiced to turn the fiber aggregates, which include dispersed and mixed binder fibers in matrix fibers, into cushion structures by the heating and the cooling process. This is to say, the cushion structures are produced by uniting the fibers with the molten binder fibers dispersed and mixed into the matrix fibers, and then the molten binder fibers act as bonding agent to adhere the fibers at their points of intersection. And by adequate selection of polymers which form both matrix fibers and binder fibers, the cushion structures made of the fiber aggregates are expected to be able to replace foamed polyurethane seats having many defects said above.
In spite of these advantages of cushion structures made of the fiber aggregate, they have disadvantage such as increasing costs, because they require much man-power and excessive time to produce them. Therefore, there are many proposals on method/apparatus to make cushion structures from the fiber aggregates in order to reduce costs and man-power.
For instance, International Patent Application WO91/18828 discloses an apparatus for producing a cushion structures in a gas-permeable mold through which suction acts on its all sides in a vacuumed filling chamber as follows; inducing air flow by said suction; transporting loosened padding fiber aggregate with accompanied air flow into the mold; filling up an inside of the gas-permeable mold with said fiber aggregate; and thereafter turning said fiber aggregate into the cushion structure throughout a heating and a cooling process.
However, such apparatus must adopts a suction means to transport the fiber aggregate into a gas-permeable mold accompanied with air flow, which is induced by a suction which acts on the mold, because of this reason said apparatus has serious disadvantages as follows.
First, when mold cavity has more complicated shape (especially, when it has the shape getting deeper), it is very difficult to fill up the each portion of the mold cavity with the fiber aggregate having desired bulk density. Since, when the mold cavity has longer length relative to its back part to some extend, the fiber aggregate is apt to be accumulated not only on deepest side of the mold cavity but also on each sides of the mold cavity on which the suction acts, and a passage through which the fiber aggregate go toward the deepest side of the mold cavity by entrainment with air flow is getting narrower and narrower, and thus the amount of the supplied fiber aggregate to the deepest side of the mold cavity is getting less and less. Moreover, in the worst case, the passage through to the deepest side of the mold cavity is completely closed by accumulated fiber aggregate on the both sides of the passage. In such a case, it is obvious that production of the excellent cushion structure, having desired bulk density and the amount thereof, is very difficult, because the fiber aggregate filled up into the mold cavity is less uniform and even has voids, so that cushion structures manufactured by said method/apparatus is fatal defect.
Secondly, said mold has no means for compressing the filled fiber aggregate actively to adjust compression rate to get the moderate bulk density after the filling step is over, because the mold is positioned in a stationary state in the filling chamber. Mainly from this reason, in such a case that different densities are required corresponding to its each portion in the cushion structure, it is no use applying said apparatus for adjusting the partial density of cushion structure.
Thirdly, it is impossible for said apparatus to stuff the mold cavity with the fiber aggregate in a state of high bulk density by a suction, because a stuffing force induced by the suction is not so stronger than that of compression air.
In U.S. Pat. No. 5,482,665 a method/apparatus is disclosed which does not depend on such suction induced by vacuum. In said patent the method/apparatus uses for introducing the fiber aggregate into a mold cavity by traversing an injector from one side to the other side of the mold cavity, so that the fiber aggregate is dispensed onto the female mold. It is sure that, by using said method/apparatus said above, the fiber aggregate can be dispensed onto the mold cavity of the female mold evenly, but they have fatal problems as follows.
First of all, in such method/apparatus, it is quite difficult to shorten the filling cycle time of the fiber aggregate into the female mold, because said method/apparatus require a injector, which traverses from the one end of the mold cavity to the other end, for filling up a mold cavity with the fiber aggregate in order not to be dispensed unevenly thereon.
Secondly, when the female mold cavity is widened, said method/apparatus require a series of injector to cover its all filling area corresponding to its widened mold cavity, and moreover, in this case, said method/apparatus require more complicated device to drive these injectors synchronized with each other in order to traverse the injectors in the same direction. And also, they require ceaseless downward air flow from the top of the female mold in order to realize evenly dispensed and accumulated state in the fiber aggregate onto the bottom cavity of the female mold.
Thirdly, the problem takes place when the mold cavity is filled up with the fiber aggregate in the height direction of the female mold, because it causes a problem that a pile of accumulated fiber aggregate is apt to collapse by the downward wind from the top of the mold. And this problem becomes more serious, as the amount of the supplied air are increased in order to accumulate the fiber aggregate more evenly onto the bottom of the mold cavity, so that the air flow becomes a turbulent flow which is difficult to rectify. Therefore, the height of the piled fiber aggregate onto the female mold is limited, so, in order to fill up as uniform as possible with the fiber aggregate in the height direction, it requires to adjust the height of the piled fiber aggregate and to average it by traversing the injectors from the one end of the mold cavity to the other end for many times. Because of this reason, it is obvious that said method requires so much time for filling up the mold cavity with the fiber aggregate, that it is no use for said method expecting time-shortened molding and cost reduction for making the cushion structure.
Fourthly, as being easily imaginable, because of requiring for the fiber aggregate to pile up in the height direction, said method has such a serious problem that it can not get the height of the piled fiber aggregate to be high or low partially. Therefore, said method for inserting the male mold into the female mold may be impossible to control a cushion structure having a desired shape to make within only one cycle time. Then, in order to partially control the bulk density of the cushion structure in its each selected portion, from a viewpoint of reduction of molding time and cost said method has a fatal problem because it requires another filling process for filling up a depression formed at a selected portion, having the higher bulk density than that of the other, with the fiber aggregate.
Despite the cushion structure made of the fiber aggregate has many advantages, in a viewpoint of cost reduction and mass production, it can not yet replace the same made of foamed polyurethane, because it take much time to turn the fiber aggregate into the cushion structure. On the other hand, said formerly, a cushion structure from foamed polyurethane has many problems, and also it is inferior to that from a fiber aggregate in its performance and character. Therefore, up to now, in spite of having a lot of excellent performance the cushion structures from the fiber aggregate have not been largely produced on a commercial scale for the use of the seat material of automobile, airplane, etc.